# Angular spread between two colour light (refraction)

1. Aug 9, 2010

### 8uhohs

Hi, I know i've seen this question on this site before, but it didn't explain how to do it. I don't even know where to begin...

Q: Consider the optical interface between crown glass and ethanol.

b) White light travels from crown glass into ethanol. If the angle of incidence in crown
glass is 60.00 degrees, what is the angular spread between the red and violet parts of the visible spectrum in the ethanol? Illustrate your
answer with a light-ray diagram.

index of refraction:
red light in crown glass - n=1.520
violet light in crown glass - n=1.538
red light in ethanol - n=1.363
violet light in ethanol - n=1.376

I think I'm suppose to use Snell's Law...but don't know how. Thanks in advance for your help

2. Aug 9, 2010

### rl.bhat

Angle of incidence is given. find angle of refraction for red and violet color in the crown glass.

These angle of refractions become angle of incidence for the crown-ethanol interface.

Now find the angle of refraction in the ethanol for red and violet by using

n1*sinθ1 = n2*sinθ2.

Τhe angular separation = θ2 - θ1.

3. Aug 9, 2010

### 8uhohs

do i find the angle of refraction for red and violet in the crown glass with n1*sinθ1 = n2*sinθ2 also???

here's my attempt..i think it's wrong though, because what i'm not sure w/ is what do i put for n2 in the equations...

crown glass: n=1.52
ethanol: n=1.36

red:
sinθ2=(n1*sinθ1)/n2
=(1.520)(sin60.0)/1.52(?)
θ2=60.0degrees

violet:
sinθ2=(n1*sinθ1)/n2
=(1.538)(sin60.0)/1.52
θ2=61.2degrees

then,

red:
sinθ2=(n1*sinθ1)/n2
=(1.52)(sin60.0)/1.36
θ2=75.4degrees

violet:
sinθ2=(n1*sinθ1)/n2
=(1.538)(sin61.2)/1.36
θ2=82.3degrees

Τhe angular separation = θ2 - θ1
=82.4-75.4
=7 degrees

Thank you for the help!!~

4. Aug 9, 2010

### rl.bhat

In the first case light is traveling from air to crown glass.

So for red light sin60 = 1.52sinθ2.

In the second case 1.52sin(θ2) = 1.36sin(θ3)

Similarly try for violet light.

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